1. Field of Invention
This invention relates generally to adjustable lighting and, more particularly, to adjustable lighting for displaying products in a retail environment.
2. Background Art
Various types of lighting sources are utilized in retail environments in areas where products are displayed including, for example, various lighting sources are utilized in display cases, such as for example fluorescent or LED lighting. The color of the lighting or the color temperature of white light may effect how a product appears. One type of lighting is a light-emitting diode (LED) which is a semiconductor device that emits incoherent narrow-spectrum light when electrically biased in the forward direction. This effect is a form of electroluminescence. The color of the emitted light depends on the chemical composition of the semiconducting material used, and can be near-ultraviolet, visible or infrared LED lighting.
An LED is a special type of semiconductor diode. Like a normal diode, it consists of a chip of semiconducting material impregnated, or doped, with impurities to create a structure called a p-n junction. As in other diodes, current flows easily from the p-side, or anode to the n-side, or cathode, but not in the reverse direction. Charge-carriers—electrons and holes-flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon as it does so.
The wavelength of the light emitted, and therefore its color, depends on the bandgap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes recombine by a non-radiative transition which produces no optical emission, because these are indirect bandgap materials. The materials used for an LED have a direct bandgap with energies corresponding to near-infrared, visible or near-ultraviolet light.
LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have made possible the production of devices with ever shorter wavelengths, producing light in a variety of colors. LED lights are a very versatile low engery lighting that provides sufficient intensity in various colors.
Lighting systems are used to illuminate display cases as well as other retail display areas, such as commercial refrigeration units and displays, as well as other display cases that need not be refrigerated. Fluorescent tubes are quite often used to illuminate products disposed in a display case or some other open display area in a retail store. However, fluorescent tubes do not last nearly as long as a typical LED and consume more power than LEDs. Furthermore, for refrigerated display cases, initiating the required arc to illuminate a fluorescent tube can be difficult in a refrigerated compartment. Also, LEDs have more flexibility in color choice and color temperature for white light without the use of color filters.
The selection for color of lighting and even the color temperature of white light is important when displaying a product because the color of display lighting can effect the appearance of an item on display. White light is typically utilized to display products in a retail environment, however, even various white light sources will have various color temperature or color hues.
“White light” is commonly described by its color temperature. A traditional incandescent light source's color temperature is determined by comparing its hue with a theoretical, heated black-body radiator. The lamp's color temperature is the temperature in kelvins at which the heated black-body radiator matches the hue of the lamp.
How human beings perceive objects can be effected by the light source and the associated color of the light source. Many retailers are accustomed to controlling the lighting source and corresponding color in a product display environment. Retailers often times attempt to engineer the lighting environment inside a structure to emulate an ideal and a perfect set of lighting conditions to best display a given product. However, different products display better under different lighting conditions, thus it is difficult to find one lighting that will work for all types of products.
The desire to control the properties of light in an artificial environment is easy to understand. Humans are primarily visual creatures. The human eye requires light to see by and our eyes are particularly sensitive to color. Therefore, a given product may appear to be more appealing to the human eye when displayed under certain light conditions. However, the configuration and placement of products in a retail environment changes often, but it can be difficult to change the lighting in a given environment every time a product configuration changes.
Visible light is a collection of electromagnetic waves (electromagnetic radiation) of different frequencies, each wavelength of which represents a particular “color” of the light spectrum. Visible light is generally thought to comprise those light waves with wavelength between about 400 nm and about 700 nm. Each of the wavelengths within this spectrum comprises a distinct color of light from deep blue/purple at around 400 nm to dark red at around 700 nm. Mixing these colors of light produces additional colors of light. The distinctive color of a neon sign results from a number of discrete wavelengths of light. For example, these wavelengths combine additively to produce the resulting wave or spectrum that makes up a color. One such color is white light.
Because of the importance of white light, and since white light is the mixing of multiple wavelengths of light, there have arisen multiple techniques for characterization of white light that relate to how human beings interpret a particular white light. The first of these is the use of color temperature, which relates to the color of the light within white. Correlated color temperature is characterized in color reproduction fields according to the temperature in degrees Kelvin (K) of a black body radiator that radiates the same color light as the light in question. The color temperature of viewing light depends on the color content of the viewing light.
The second classification of white light involves its quality. In 1965 the Commission Internationale de l'Eclairage (CIE) recommended a method for measuring the color rendering properties of light sources based on a test color sample method. This method has been updated and is described in the CIE 13.3-1995 technical report “Method of Measuring and Specifying Colour Rendering Properties of Light Sources,”. In essence, this method involves the spectroradiometric measurement of the light source under test. This data is multiplied by the reflectance spectrums of eight color samples. The resulting spectrums are converted to tristimulus values based on the CIE 1931 standard observer. The shift of these values with respect to a reference light are determined for the uniform color space (UCS) recommended in 1960 by the CIE. The average of the eight color shifts is calculated to generate the General Color Rendering Index, known as CRI.
Artificial lighting generally uses the standard CRI to determine the quality of white light. If a light yields a high CRI compared to full spectrum white light then it is considered to generate better quality white light (light that is more “natural” and enables colored surfaces to be better rendered). This method has been used since 1965 as a point of comparison for all different types of light sources.
Current lighting technology makes such adjustment and control difficult, because common sources of light, such as halogen, incandescent, and fluorescent sources, generate light of a fixed color temperature and spectrum. Further, altering the color temperature or spectrum will usually alter other lighting variables in an undesirable way. For example, increasing the voltage applied to an incandescent light may raise the color temperature of the resulting light, but also results in an overall increase in brightness.
In artificial lighting, control over the range of colors that can be produced by a lighting fixture is desirable. Many lighting fixtures known in the art can only produce a single color of light instead of range of colors. That color may vary across lighting fixtures (for instance a fluorescent lighting fixture produces a different color of light than a sodium vapor lamp). The use of filters on a lighting fixture does not enable a lighting fixture to produce a range of colors, it merely allows a lighting fixture to produce its single color, which is then partially absorbed and partially transmitted by the filter. Once the filter is placed, the fixture can only produce a single (now different) color of light, but cannot produce a range of colors.
In control of artificial lighting, it is further desirable to be able to specify a point within the range of color producible by a lighting fixture that will be the point of highest intensity. An incandescent light fixture can produce a range of colors, but the intensity necessarily increases as the color temperature increases which does not enable control of the color at the point of maximum intensity. Filters can be used but lack control of the point of maximum intensity, as the point of maximum intensity of a lighting fixture will be the unfiltered color (any filter absorbs some of the intensity).
The correlated color temperature, and CRI, of viewing light can affect the way in which an observer perceives a color image of a product on display. An observer will perceive the same color image of the product differently when viewed under lights having different correlated color temperatures. For example, a color image of a product, which looks normal when viewed in early morning daylight will look bluish and washed out when viewed under overcast midday skies. Further, a white light with a poor CRI may cause colored surfaces to appear distorted.
Applicants have further appreciated that the color temperature of ambient light affects how viewers perceive a display, such as a retail or marketing display, by changing the perceived color of such items as foods, clothing apparel, furniture, jewelry and other products containing visual elements that can greatly affect how people view and react to such displays. Variations in the color temperature of lighting can affect how appealing or attractive such a display may be to customers.
Moreover, the ability to view a decoratively patterned or colored item in a lighting environment or color temperature condition which matches or closely approximates the conditions under which the item will normally be viewed would permit such colored items to be more accurately viewed. Typically, the lighting used in a retail display setting cannot be varied and is often chosen to highlight a particular facet of the color of the item leaving a purchaser to guess as to whether the item in question will retain an attractive appearance under the lighting conditions where the item will eventually be placed.
Various systems and methods for changing and/or generating and/or modulating illumination conditions to generate light of a desired and controllable color, for creating lighting fixtures for producing light in desirable and reproducible colors, and for modifying the color temperature or color shade of light produced by a lighting fixture within a specified range have been utilized. However, the products being displayed in open display areas or in the display cases in a retail environment may change frequently, which will require the retailer to implement a lighting adjustment to accommodate the different product type.
An automated system and method is needed to adjust the lighting in a display area or display case when product changes occur.